Abstract

DEMARTIS, Manuel et al. Granitic pegmatites emplacement from southern Comechingones pegmatitic field, Córdoba. Rev. Asoc. Geol. Argent. [online]. 2010, vol.67, n.4, pp.536-544. ISSN 0004-4822.

Southern Comechingones pegmatitic field is composed of  zoned be-Nb-Ta-u−granite pegmatites with mostly lenticular morphologies, hosted in mylonitic rocks of  the Guacha Corral shear zone. Important orientation changes in the host rock mylonitic foliation were identified, thus defining an anastomosed general pattern of  the shear zone both at the outcropping and regional scale. Pegmatites were mostly conformably emplaced within mylonitic foliation. discordant pegmatites were also described. An internal planar fabric defined by the orientation of  quartz, feldspar and muscovite from the intermediate zone of  the granitic pegmatites was developed during the Guacha Corral shear zone deformation. Mineral stretching lineations in pegmatites generally coincide with that of  the mylonitic host rocks. Structural analysis suggest that pegmatites of  the Comechingones pegmatitic field were emplaced synkinematically with the ductile amphibolite facies deformational event of  the Guacha Corral shear zone, developed under progressive simple shear deformation. Almost pure reverse sense of  shear with westward tectonic transport characterized this deformational event, developed during Famatinian orogeny. Anastomosed general pattern of  the mylonitic foliation in the Guacha Corral shear zone was the responsible for the origin of  the spaces in which pegmatites and granites emplaced. These rocks then cooled and crystallized simultaneously with progressive deformation. Moreover, discordant pegmatites constitute Riedel shear model T extensional fractures, and represented ascent magma channels. These structures would have been progressively sheared and rotated from their original orientation, until they were subparalell to the enclosing mylonitic foliation, outcropping at present time as almost conformably pegmatites.

Keywords : Emplacement; Comechingones pegmatitic field; Guacha Corral shear zone.

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